1. Field of the Invention
The present invention relates to a signal processing circuit for a solid-state imaging device of a portable telephone with a built-in camera, a digital still camera, etc., and to a solid-state imaging device.
2. Description of the Related Art
Imaging devices such as a portable telephone, digital still camera and the like have an enlargement zoom mechanism mounted thereon as an essential function of the camera. As the enlargement zoom functions, there are an optical enlargement zoom function that zooms in and out by controlling a lens, and an electronic enlargement zoom mechanism that zooms by interpolation of digital data. The optical enlargement zoom mechanism tends to be large-scaled since it requires mechanisms such as a zoom lens and a motor to drive the zoom lens. Therefore, an electronic enlargement zoom mechanism of a smaller-scale is frequently used for a small-size imaging device such as a portable camera.
A picture image captured by the electronic enlargement mechanism will be described by referring to FIG. 9 and FIG. 10. First, there will be described the case where electronic enlargement zoom is performed without using a frame memory. As shown in FIG. 9A, let us look into the case where: an output picture area 82 is smaller than a picked-up area 81 captured by the solid-state imaging device. For example, when an image of QVGA (320 pixels×240 lines) output image size is outputted by the solid-state imaging device having the picked-up picture area of 1,280 pixels×960 lines, the picked-up picture is reduced by one fourth to obtain the one-times (unmagnified) output picture (¼×4=1). Accordingly, an output picture of four third magnification can be obtained with a reduction rate of one third, and the output picture of twice the size can be obtained with the reduction rate of one half. Enlargement zoom can be achieved in this way. As shown in FIG. 9B, the maximum enlargement rate is the four times ( 1/1 reduction rate), which corresponds to the case where a subject area 83 picked up by the solid-state imaging device is cut out in an output picture size of QVGA (picked-up output area 84 of the output picture).
However, it is not possible with this configuration to perform enlargement zoom when the size of the picked-up area 91 and that of the picked-up picture output area 92 are equal as shown in FIG. 10A. In such a case, as shown in FIG. 10B, enlargement zoom can be achieved by storing the picked-up data of a part of a subject area 93 in one scene to a frame memory and carrying out electronic interpolation (output picture area 94). However, the frame memory is required additionally in such a case.
As described above, there is additionally required the frame memory for performing the electronic enlargement zoom when the ratio between the picked-up size and the output size (output size/picked-up size) is 1 or more. Particularly in the case of a small-size portable apparatus, it is essential to downsize the camera module and keep the low-cost. Thus, it is not practical to mount the frame memory.
In addition to a CCD sensor, there is also an MOS-type sensor as the imaging sensor. The MOS-type sensor is characterized by a low power consumption, a single power drive, etc., and used frequently for a small-size portable apparatus such as a portable telephone with a built-in camera. However, like the CCD, the MOS-type sensor faces the above-described problems.